Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) remove material from the surface of semiconductor wafers, field emission displays or other microelectronic substrates in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a CMP machine 10 with a platen 20, a carrier assembly 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 attached to an upper surface 22 of the platen 20 and the lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F), or it reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The carrier assembly 30 has a head 32 to which a substrate 12 may be attached, or the substrate 12 may be attached to a resilient pad 34 in the head 32. The head 32 may be a free-floating wafer carrier, or an actuator assembly 36 may be coupled to the head 32 to impart axial and/or rotational motion to the substrate 12 (indicated by arrows H and I, respectively).
The planarizing pad 40 and a planarizing solution 44 on the pad 40 collectively define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing pad 40 can be a soft pad or a hard pad. The planarizing pad 40 can also be a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution 44 is typically a non-abrasive “clean solution” without abrasive particles. In other applications, the planarizing pad 40 can be a non-abrasive pad composed of a polymeric material (e.g., polyurethane), resin, felt or other suitable materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically abrasive slurries with abrasive particles suspended in a liquid.
To planarize the substrate 12 with the CMP machine 10, the carrier assembly 30 presses the substrate 12 face-downward against the polishing medium. More specifically, the carrier assembly 30 generally presses the substrate 12 against the planarizing liquid 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier assembly 30 move to rub the substrate 12 against the planarizing surface 42. As the substrate 12 rubs against the planarizing surface 42, material is removed from the face of the substrate 12.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns. During the construction of transistors, contacts, interconnects and other features, many substrates develop large “step heights” that create highly topographic surfaces. Such highly topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on topographic surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical surface into a highly uniform, planar surface at various stages of manufacturing microelectronic devices on a substrate.
In the highly competitive semiconductor industry, it is also desirable to maximize the throughput of CMP processing by producing a planar surface on a substrate as quickly as possible. The throughput of CMP processing is a function, at least in part, of the polishing rate of the substrate assembly and the ability to accurately stop CMP processing at a desired endpoint. Therefore, it is generally desirable for CMP processes to provide (a) a uniform polishing rate across the face of a substrate to enhance the planarity of the finished substrate surface, and (b) a reasonably consistent polishing rate during a planarizing cycle to enhance the accuracy of determining the endpoint of a planarizing cycle.
One concern of CMP processing using soft pads is that they may not produce a flat, planar surface on the workpiece because they may conform to the topography of the workpiece. Soft pads also have a relatively short life span because the conditioning devices and the abrasive slurries wear away soft pads. Therefore, many current planarizing applications use hard pads to overcome the drawbacks of soft pads.
Although hard pads can be an improvement over soft pads, hard pads can be difficult to “condition” to bring the planarizing surface into a desired state for accurately planarizing workpieces. To condition a hard pad, an end-effector having small diamond particles can be rubbed across the surface of the planarizing pad to form microscratches in the pad surface. However, the microscratches are generally formed in a relatively random pattern because the diamond end-effector is swept across the pad surface while the pad rotates. The conditioned surface can vary, which can cause variances in planarizing results throughout a run of wafers or from one pad to another. Moreover, the diamond particles on the end-effector may break off during the conditioning cycle, which can produce defects in the planarizing pad or remain on the planarizing pad during a planarizing cycle and produce defects in the wafers. Hard polishing pads can accordingly be difficult to maintain.
A serious concern of using hard pads with raised microfeatures is that conditioning the planarizing surface with a diamond end-effector can significantly alter the size and shape of the raised features. The desired microfeatures on hard polishing pads are arranged in patterns with very precise sizes, shapes and spacings between the microfeatures. It will be appreciated that abrading the bearing surfaces of the microfeatures may alter the size and shape of the microfeatures in a manner that alters the planarizing characteristics of the polishing pad. Therefore, it would be desirable to develop a process for conditioning hard polishing pads in a manner that preserves the integrity of the planarizing surface.